Characterization of the interfacial interactions between microparticles and surfaces using piezoelectric sensors

Abstract

Applications of microparticles and nanoparticles have been found in the fields of microelectronics, micro-electro-mechanical systems (MEMS), material engineering, chemical engineering, biomedical engineering and others. In most of the applications, the interfacial interactions of microparticles and nanoparticles with surfaces play a significant role. Currently, there are a very limited number of techniques capable of characterizing the properties of both the particles and the particle-surface interactions in real time with high sensitivities. In this thesis, a novel method using a thickness shear mode (TSM) acoustic wave sensor is devised to characterize the interactions of microparticles with surfaces and the properties of microparticles.Interfacial forces between a single microparticle and a surface, including Van der Waals forces, the gravitational force and capillary force, are analyzed. A mechanical model is developed to describe the interfacial interaction of a single microparticle with a piezoelectric quartz crystal TSM sensor. An important parameter, interfacial coupling coefficient, is proposed to characterize the particle-surface interactions. Equivalent electrical circuits are built to study the effects of a loading of a single or multiple particles on the electrical characteristics of a TSM sensor. The dependence of the change in the resonant frequency of a TSM sensor on the diameter of a particle is obtained. The mass sensitivity of 5 MHz and 10 MHz TSM sensors are experimentally determined. The interfacial coupling coefficients obtained from the TSM measurements are compared with the results obtained from the measurements of the interaction forces between a particle and a surface by using an atomic force microscope (AFM).This study shows that TSM sensors can be used as a very promising tool for the real-time characterization of the interactions of microparticles with a surface and the properties of the microparticles.%%%%Ph.D., Electrical Engineering – Drexel University, 2006